<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 
        用逗号隔开
        */
        .box,
        h3.title,
        p.title{
            color: red;
        }

    </style>
</head>
<body>
    <div class="box">我是box</div>
    <h3 class="title">我是h3.title</h3>
    <p class="title">我是p.title</p>
    <div><span>我是span</span></div>
</body>
</html>